The present invention provides novel compositions, methods of their use and methods of their manufacture, such compositions generally useful as agents in the construction and building trades. More specifically, the compounds of the present invention can be used in construction and building applications that benefit from a relatively lightweight, extendable, moldable, pourable cementitious material that has high strength, good insulation properties and vermin resistance properties. At the present time, there is a need in the area of construction and building for such agents.
In the field of preparation and use of lightweight cementitious materials, such as so-called lightweight aggregates the materials that have been available to the trades up until now have generally required the addition of various constituents to achieve a strong but lightweight concrete mass that has a high homogeneity of constituents and which is uniformly bonded throughout the mass. Of the methods known to the inventor, there have been several patents issued relating to the inclusion of expanded polystyrene beads of an average bead size of about 20 mm diameter (about 20,000 microns) that are expanded by various heating methods either before the beads are introduced into the concrete mixture, or expanded after they have been added to the concrete mixture. It is an object of this invention to provide for a pourable, lightweight cementitious mixture that does not rely on expanded polystyrene for weight saving properties and strength. It is another object of the present invention to provide for a pourable, lightweight cementitious mixture that can be used in the construction of molded roofing tiles. It is yet another object of the present invention to provide for a pourable, lightweight cementitious mixture that can be used in the construction of laminated building foundations, that is, the type of foundations in which a cement pour product is poured in between form walls that become part of the structural assembly upon curing of the cement. It is yet another object of the present invention to provide for a pourable, lightweight cementitious mixture that resists insect infestation and deterioration. Yet another object of the present invention is to provide for an extendable cementitious mixture that can be extruded through various extrusion dies and can be cured without further shape manipulation or formation. Still another object of the invention is to provide for a cementitious mixture that can be molded under high pressure and readily ejected from the mold with a minimum of green time to enable rapid re-cycling of the mold. Still one more object of the invention is provide a synthetic aggregate by curing and crushing a compressed product of an aqueous cementitious mixture.
The last of the foregoing objects of the present invention, i.e. the production of a synthetic or man-made aggregate, is achieved by curing and then crushing a compressed product made from an aqueous cementitious mixture comprising cement and at least one member selected from the group consisting of bottom ash and non-cementitious fly ash. Other additives such as polystyrene for reducing the weight of the compressed product but not its strength may also be added to the mixture. Prior to crushing, it is also important to cure the compressed product so that it has a compressive strength of at least 600 psi. Once cured, the compressed product is crushed into fragments of a size which are capable of passing through mesh screen having sieve openings ranging from between about 19 mm and 75 microns. The crushed fragments now referred to herein as a synthetic or man-made aggregate is suitable for a multiplicity of uses such as for mixing with a cementing material to form concrete, mortar or plaster. Other uses include use as a filler and as a filtration media.
The invention comprises lightweight load bearing cementitious compositions that yield building materials having a density of 35 to 80 lb/ft3, comprising from 40 to 99% by volume of aqueous cementitious mixture and from 0 to 60% by volume of micronized polystyrene foam particles, the foam particles having a minimum density of 1.0 lb/ft3, and the water content of the aqueous cementitious product being present in a range of from 0.005 to 20% by volume. A more preferred range of water content is from 0.005% to 5% by volume, more preferably from 0.005% to 2% by volume. Preferred ranges of cementitious mixtures and micronized polystyrene foam particles are from 40 to 75% by volume cementitious mixtures and 25 to 60% by volume foam. More preferred ranges of cementitious mixtures and micronized polystyrene foam particles are from 50 to 60% by volume cementitious mixtures and 40 to 50% by volume foam.
The term xe2x80x9caqueous cementitious mixturexe2x80x9d refers to any of a number of compositions comprising water, a cement material, and one or more fillers or adjuvants that form a slurry that hardens upon curing. Cement materials include hydraulic cements, lime, and the like. Adjuvants and fillers include bottom ash, fly ash, aggregate, air entrainment agents, crushed glass, recycled plastic, colorant agents and so forth. The compositions of the invention include a class of low water weight cement mixtures that have only from about 0.005 to 5% v/v of water added to the final mix. Such low water compositions have surprisingly been found to produce plastic cement mixtures that are readily processed through an extrusion die into a shape that needs no additional manipulation or molding after having been cut off subsequent to exiting the extrusion die. Also, the low water content compositions are well suited to being molded under high pressure, (e.g. in the range of five hundred to five thousand lb/in2). The advantage of such high pressure molding operations is that after removing the pressure, the molded article can be ejected from the mold very quickly, usually after three to twenty seconds or so, thereby allowing the mold to be available for another cycle of molding another article. Ordinarily, when a plastic composition is being shaped in a mold, there is some period of time that the composition must remain in the mold until it has sufficiently hardened to at least remove it from the mold, a period known in the trade as xe2x80x98green timexe2x80x99. The longer the green time of a given composition being used to mold articles, the fewer times the mold itself can be cycled during a work day. The extrusion and high pressure molding techniques and apparatus used in fabricating products out of the compositions of the invention are well known to those of ordinary skill in the art, and do not form a separate part of the invention as claimed herein, except to the limited extent they are a step in the process of making aggregate and articles out of the compositions of the invention. The compression stage of working with the compositions of the invention causes the material to be compressed down to approximately one third of its original volume. It has been found that articles molded out of these compositions lose the brittle quality of most molded cement or concrete compositions. For example, a roof tile pressure molded or extruded from these compositions doesn""t shatter if dropped on the floor from a height of about three to four feet.
The term xe2x80x9ccementxe2x80x9d as defined herein refers to inorganic materials combined with water to form a hydrated bonded matrix. Hydraulic cement undergoes a hydration reaction in the presence of a sufficient quantity of water that produces the hardened product. The following are some typical hydration reactions:
Ca3Al3O6+6H2O, Ca3Al2(OH)12;
Ca2SiO4+xH2Oxe2x80x94Ca2Si)4xe2x80x94xH2O;
Ca3SiO5+(x+1)H2O E Ca2SiO4xe2x80x94xH2O+Ca(OH)2
The most preferred hydraulic cement for use in the invention is portland cement. Various embodiments of the invention call for the addition of lime (calcium oxide) which is itself also a hydraulic cement. Micronized polymeric particles comprise the weight saving component of the present invention, and can be polystyrene, polyester, polyethylene, polypropylene, acrylic, polyisocyanurate, polyacrylamide, polyacrylimide, mixed imide-amides arylamides, arylimides and the like. The most preferred material is polystyrene. Micronized polystyrene foam particulates are the result of a process of shredding virgin, and/or recycled polystyrene foam, and give the final product its lightweight characteristics. The most preferred form of micronized polystyrene foam particulates is made up of virgin polystyrene foam of approximately 1 to 5 lb/ft.sup.3 density that has been treated with a borate. The borate acts as a potent insect repellant, tending to keep vermin insects away from the rest of the structure of the building that incorporates such borate-containing cement compositions. This is to be distinguished from the use cementitious compositions as a means of disposing of waste insecticides, including borate. Alternatively, a borate such as TIM-BOR.RTM. brand of borate available from U.S. Borax Co. can be added in powder form to the cementitious mixture.
Such foam block is then shredded to provide the micronized particles having irregular surfaces. A particularly well suited method of shredding is by running an electrified fine gauge wire through solid blocks of this foam, according to methods well known to those of ordinary skill in cutting and fabricating such polystyrene foam blocks. Alternatively, a wire brush can be used to brush against and abrade a solid foam block, thereby producing the desired small particulates of foam. This type of product is also generally available as a waste by-product (xe2x80x9cfinesxe2x80x9d) at facilities that cut virgin polystyrene foam block. This process produces micronized foam particulates that can be characterized by sieve analysis in general conformance with ASTM C 136, entitled xe2x80x9cSieve Analysis of Fine and Coarse Aggregatesxe2x80x9d. Such method of analysis is suitable for particles of from 50 to 5,000 microns in size. A more preferred range of foam particle size is from 50-2000 microns, more preferably from 600-1200 microns. A typical sample yielded the following sieve analysis:
From this analysis, it can be seen that the micronized polystyrene foam particulates preferred in the invention can be characterized as a coarse to moderately coarse powder, as those terms are used in the science of rheology, having a median particle size of approximately 800 microns. Micronized foam of this type is available from the R-Control Co. of Denver, Colo., and other major cities or from Poudre Plastics of Fort Collins, Colo.
Fly ash of the cementitious type can be used as a partial replacement for portland cement in concrete construction, and it is generally accepted that the proportion of portland cement replaced by the usual fly ash should not exceed about 20% to avoid significant reduction in the compressive strength or the resultant concrete. Fly ash components of the cementitious mixtures of the invention can be either C-type (xe2x80x9cC-classxe2x80x9d) or F-type (xe2x80x9cF-classxe2x80x9d) fly ash. Fly ash is the very finely divided ash produced by the combustion of anthracite and bituminous coal in large industrial coal-fired boilers, especially for the steam generation of electricity, that is suspended in the flue gases from such boilers and is separated therefrom by means such as electrostatic precipitation. This fly ash is an extremely finely divided material generally in the form of spherical bead-like particles, with at least 70% by weight passing a 200 mesh sieve and has a generally glassy state, resulting from fusion or sintering during combustion. As recognized in the American Society of Testing Materials (ASTM) specification designation C618-85 entitled xe2x80x9cFly Ash and Raw or Calcined Natural Pozzolan for Use as a Mineral Admixture in Portland Cement Concretexe2x80x9d, cementitious fly ash is subdivided into two distinct classifications; namely, Class F and Class C. The definitions of these two classes are as follows: xe2x80x9cClass F-Fly ash normally produced from burning antharacite or bituminous coal that meets the applicable requirements for this class as given herein. This class fly ash has pozzolanic properties. Class C-Fly ash normally produced from lignite or subbituminous coal that meets the applicable requirements for this class as given herein. This class of fly ash, in addition to having pozzolanic properties, also has some cementitious properties. Some Class C flyashes may contain lime contents higher than 10%.xe2x80x9d The reference to xe2x80x9cpozzalanic propertiesxe2x80x9d refers to the capability of certain mixtures, which are not in themselves cementitious, of undergoing a cementitious reaction when mixed with lime (calcium oxide) in the presence of water. Class F Fly-ashes can have from 4 to 9% calcium oxide contents, while Class C Fly-ashes can have from 30 to 60% calcium oxide contents. For this reason, Class C fly ash possesses direct cementitious properties as well as pozzolanic properties. Fly ash is readily available from local building products outlets. Fly ash that has been de-limed, which is called for in several embodiments of the cementitious compositions of the present invention, is also readily commercially available from a variety of local sources.
Bottom ash which is employed as a constituent in forming the aggregate of the present invention is also a byproduct produced by the combustion of anthracite and/or bituminous coal. Bottom ash is actually a residue of the combustion process which collects in the bottom of the boiler or generator as the coal is burned. Bottom ash has a similar chemical makeup to fly ash but a much coarser gradation. It typically contains SiO2, Al2O3, Fe2O3. CaO, MgO, Na2O, K2O, TiO2, MnO2, P2O5, SrO, BaO and SO3. However, its composition may vary from plant to plant depending of the actual type of coal burned, the humidity and other factors as well. Bottom ash has little to no cementitious properties. Further information regarding bottom ash and its uses are disclosed in articles entitled xe2x80x9cCoal Bottom Ash/Boiler Slagxe2x80x9d (author unknown) and xe2x80x9cThe Use of Recycled Materials in Highway Constructionxe2x80x9d by Robin L. Schroeder, both of which are published on the Turner-Fairbank Highway Research Center""s web site at www.tfhrc.gov.
There is also a type of fly ash which has little or no cementitious properties which may also be used in producing the aggregate of the present invention. Non-cementitious fly ash is typically separated out from the cementitious fly ash at the plant as is well known to those skilled in the art. The composition of such non-cementitious fly ash will also vary depending of the actual type of coal burned, the humidity and other factors known to those in the art.
The presence of an air entraining agent helps to create air cells or voids in a batch of concrete, which can help to maintain good workability of fresh concrete and also improve the durability to freezing and thawing of hardened concrete. Air entrainment agents include anionic surfactants such as polyoxyethylene alkyl ether sulfates or polyoxyethylene alkly phenyl ether sulfates or salts thereof, polyoxyethylene alkyl ether phosphates or polyoxyethylene alklyl phenyl ether phosphates or salts thereof, alkylbenzenesulfonic acids or salts thereof, alpha-olefinic-sulfonic acids or salts thereof, fatty acids or salts thereof, polyoxyethylene polyalcohol fatty acid esters, polyethylene glycol fatty acid esters, polyoxyethylene pentaerythryritol fatty acid esters and polyoxyethylene sorbitan fatty acid esters and the fatty acids or salts thereof.
Sand is frequently used to expand the volume of cementitious mixtures. Sand used in the cementitious mixtures of the present invention include play sand whether from beach or river sources, and silica sand. Clay is a suitable alternative for sand in the mixtures of the invention. An especially preferred volume expansion material is expanded shale, clay and slate mix (ESCS). This material is a ceramic lightweight aggregate prepared by expanding select minerals in a ritary kiln at 1000 degrees celsius or more. This process results in a light weight, inert material comprised of a mix of oxides including SiO2, Al2O3, Fe2O3, CaO, MgO, K2O, N2O, SO3, P2O5, TiO2, Mn2O3, and CO2. This material is available through the Expanded Shale, Clay and Slate Institute, Salt Lake City, Utah, which makes a list available of distributors of this material throughout the United States. The use of ESCS can completely replace sand in the cementitious mixtures of the invention, and produce an especially light final product in concert with the foam particles described above.
As a means of reinforcing the product, reinforcement fibers can be added to the cementitious mixtures of the invention. Such fibers act as reinforcing components, having a large aspect ratio, that is, their length/diameter ratio is high, so that a load is transferred across potential points of fracture. Typical preferred materials are fiberglass strands of approximately one to one and three fourths inches in length, although any material can be used that has a higher Young""s modulus than the matrix of the cementitious material. Another preferred fiber are commercially available from the Fibermesh company of Chatanooga, Tenn., and are comprised of polypropylene fiber. In those embodiments of the invention that include the use of reinforcing fibers, the final molded product often displays a hair-like external appearance. Such extraneous fiber hairs can be burned off with a suitable torch.
Densities of products using the compositions of the present invention can vary from 60 to 115 lb/ft3, preferably 35-90 lb/ft3, with many products being about 50 lb/ft3.
The compositions of the invention are well suited to the fabrication of molded construction materials, especially roofing tiles and foundation walls. The compositions are easier to pour than regular weight mixtures and exhibit greater strength. The compositions can be readily cast into molds according to methods well known to those of skill in the art for roofing tiles in virtually any three dimensional configuration desired, including configurations having certain topical textures such as having the appearance of wooden shakes, slate shingles, or smooth faced ceramic tiles. A typical shingle can have approximate dimensions of ten inches in width by seventeen inches in length by one and three-quarters inches in thickness. In the molding of roofing materials, the addition of an air entrainment agent makes the final product more water resistant.
When foundation walls are poured using the lightweight cementitious compositions of the invention, the walls can be taken above grade due to the lighter weight. Ordinarily, the lower part of the foundation wall has a tendency to blow outwards under the sheer weight of the concrete mixture, but the lighter weight of the compositions of the invention tend to lessen the chances of this happening. Foundation walls prepared using these compositions can readily take conventional fasteners used in conventional foundation wall construction. A particularly preferred type of foundation wall construction calls for the use of foam plastic walls to form a sandwich containing the poured lightweight concrete. After hardening, the foam walls are left intact to add significantly to the insulation properties of the foundation walls. Such walls can be made of extruded polystyrenes or the like, and frequently are available to contractors in preformed wall and corner units that snap or clip together, according to methods well known to those in the construction trades.
Additionally, the cementitious compositions of the invention can be used as a stucco or as a plaster, being applied by any means well known to those of ordinary skill in those trades; as a wall board, of the sandwich type of construction wherein the hardened material is sandwiched by suitably strong paper or other construction material; as pavers for sidewalks, roofs, driveways and the like; as a pour material for sidewalks, driveways and the like; as a monolithic pour material for floors of buildings; as molded chimney stacks or smoke stacks; as bricks; as fire or refractory bricks for fireplaces, furnaces, crucibles and the like; as roof pavers; as monolithic pour material for radiant heat floor systems; as blocks for landscape retaining walls; as prestressed concrete wall systems; as tilt-up wall systems, i.e. where a wall component as poured on site and then tilted up when hardened; and as mason""s mortar.
A stucco preparation means a finish for walls, made from sand, lime and cement mixed with water, that, as a covering for walls, is applied wet and dries hard and durable to form a rough finish for exterior walls.
A paver is a brick molded so as to be easily laid down upon a substantially horizontal roadbed or walkway surface to form an upper surface that can support foot or vehicular traffic. Pavers find common use in construction of walkways and driveways. A roof paver is a particularly thin type of paver that can be used as a roofing material, assuming that the builder has built a substantial enough framework of roof rafters. Roof pavers are also known as cement shingles, and are sometimes molded and colored so as to imitate the appearance of slate shingles wood shingles, or ceramic shingles. They are sometimes reinforced with fibers.
A plaster preparation is a mixture of cementitious materials and water that forms a plastic mass that is used as a finish for walls, like stucco is applied wet and dries hard and durable to form a rough or fine finish for interior walls.
A pour product for the pouring of building floors refers to a cement and water mixture that can be poured into molds defining the floor of a building room or section, so that when the mass dries and hardens, a usable, load-beating floor is formed. A pour product for the pouring of radiant heat floors is similar except that the builder has laid down hollow tubing in the mold area defining the floor to be poured. The tubing is intended to conduct heated liquids, typically water. On top of the tubing, wet pour product is poured. The mass subsequently dries and hardens, producing a flat smooth floor surface that has the tubing embedded within it. Hot water is then pumped through the hollow tubing, which heats the entire hardened floor, which in turn radiates heat into the room.
A prestressed concrete wall system product is a molded, pre-formed panel or structural member made up of a concrete mixture in which embedded high-tensile steel is stretched, and then the stress is transferred to the concrete by bonding to the steel or by anchorages to the steel. Panels or structural members can be formed or molded into girders, load-bearing panels, floor sections, wall sections, and the like. In this application, applicants are claiming as a product by process, such prestressed molded products using the lightweight composition, as members to construct walls.
A tilt-up type of wall system product refers to a pre-molded or precast concrete structural member that is poured while the mold is lying down, i.e. the intended vertical wall surface is laid down horizontally. Upon drying and curing, the horizontally-oriented wall or panel member is then tilted up until it is vertically oriented and moved into place as a constituent member of a wall system of a building. Such tilt-up wall components can form foundations below grade, or wall systems above grade.
Preferred aqueous mixtures from which the aggregate product of the invention are made include any or all of those specifically set forth in the following examples. We have found that the most preferred aqueous mixtures use 4 parts cement, 2 parts water, 10 parts bottom ash and polystyrene foam in parts ranging from 0 to 40 parts. However, foam in 15 parts is the most preferred since it significantly reduces the weight of product produced and still provides high compressive strengths on the order of about 3000 psi. While these are the preferred mixtures, these are not to be construed as forming the only genus that is considered as the invention, and any combination of the mixtures"" components may itself form a genus. The following examples further illustrate details for the preparation of the mixtures of the present invention. Those skilled in the art will readily understand that known variations of the conditions and processes of the following preparative procedures can be used to prepare these compositions.
In each of the following examples, the mixes were prepared at a temperature of approximately 40 degrees Fahrenheit or above. Measurements, unless noted otherwise, are given as parts of volume to volume measures, abbreviated as v/v. Parts for these type of mixtures are most conveniently measured as cylinders of approximately 6 inches in length by 4 inches in diameter. Strength tests were conducted according to the ASTM C 39 protocol, the text of which is incorporated herein by reference.